Plastic tubes have an inherent permeability to transport of gasses and/or water vapor due to the physical properties of the plastic materials used in manufacturing such tubes. Therefore, it is especially difficult to maintain the shelf-life of evacuated plastic tubes that contain a liquid additive of the class used in connection with blood collection. It is also appreciated that deterioration of the volume and concentration of the liquid additive may interfere with the intended use of the tube. Sometimes hybrid assemblies are used for blood collection, including both a polyethylene terephthalate tube for oxygen and other gas barrier and a polypropylene tube for water barrier. Such assemblies are relatively expensive for disposable articles and are relatively difficult to recycle. While barrier properties can be improved somewhat by using more material, this too adds cost which is particularly undesirable in disposable products.
In addition, plastic tubes that are used for blood collection require certain performance standards to be acceptable for use in medical applications. Such performance standards include the ability to maintain greater than about 90% original draw volume over a one-year period, to be radiation sterilizable and to be non-interfering in tests and analysis.